Comment #4 on issue 151 by tru64ufs: Append/Prepend to existing key whose
value that grows larger than 1MB and non-existing key returns NOT_STORED
error
http://code.google.com/p/memcached/issues/detail?id=151
Dormando.
Here's what I am trying to do.
Workload: many append/prened(), a few read
1. append against non-existing key (allowed) - error ignored. no need to
check its existence
we only create key on DB read operation.
We are trying not to create too many keys so there are many append
operations to simplify logic
2. But once a key had been created, and unless there is another get()
operation, we only append.
since there are so many appends (append against non-existing key and
existing keys), we cannot do
get() on every append() NOT_STORED failure.
Again, NOT_STORED failure is ok for non-exsiting key.
3. Values only gets trims on get().
The problem with this is that once a key has been created, and workload
requires lots of append and few get,
when we get NOT_STORED, we do not know if this append() failure was due to
non-exsiting key or out-of-memory. Since there is no need to check for
existence when the key does not exist, we cannot add get() after each
append() failure. If you do, you are simply adding 1 RTT to each append
operation which doubles response time. Could be much worse if the value is
large (close to 1M)
Memcached does NOT remove the item when it fails to append/prepend with
out-of-mem error. It simply returns NOT_STORED.
Thank you, Dormando.
